Sketch99.com is now using the Google Javascript API for loading jQuery. I don't see any astounding advantages from using it yet, but I was curious so I decided to give it a try.
On the other hand, I'm not noticing any downsides, either.
UPDATE: I found a downside in that the jsapi resource is forced to never cache. If I load jQuery manually, it might take a little longer, but it can then cache for a much longer time. That's worthwhile to me.
Here are the HTTP headers for jsapi:
HTTP/1.x 200 OK Cache-Control: no-cache, no-store, max-age=0, must-revalidate Pragma: no-cache Expires: Fri, 01 Jan 1990 00:00:00 GMT Date: Mon, 22 Feb 2010 03:05:52 GMT Content-Type: text/javascript; charset=utf-8 Content-Encoding: gzip X-Content-Type-Options: nosniff X-Frame-Options: SAMEORIGIN Content-Length: 5391 Server: GSE X-XSS-Protection: 0